Arrangements for collecting and/or distributing information between a master station and a large number of data sources via serially connected telemetry modules are well known. For example U.S. Pat. No. 3,824,545 issued to Brenner and U.S. Pat. No. 3,723,971 issued to Betts et al. disclose such arrangements.
In the Brenner arrangement serially connected modules are successively activated and deactivated for predetermined lengths of time, the lengths of time for each module being determined by the component parameter of that module. This system has limits on message lengths. Also with Brenner's system, the master station loses control since the transmitting terminals of the respective modules each in succession generate all of the control signals transmitted to the next module.
Betts et al. discloses a telemetry system in which a central station is directly connected to first and last stations of a serially connected group of remote stations. The Betts et al. patent utilizes rather complex circuitry in each remote station in order to receive and respond with a message to unique multibit poll enabling and framing signals.
Other patents showing selective addressing of serially connected remote stations include U.S. Pat. Nos. 3,903,499; 3,838,313; and 3,845,472, while U.S. Pat. Nos. 3,327,289; 3,702,474; and 4,161,720 show other nonserially connected remote monitoring systems.